374 
DR. J. T. BOTTOMLEY AND MR. F. A. KING ON THERMAL 
Date. 
October 22, 1889 . 
Vacuum. 
Temperature 
of globe. 
Temperature 
of enclosure. 
Emissivity 
(defined). 
M. 
°c. 
°c. 
97-0 
63-0 
45-0 
1-37 x10~ 4 
1•23 x10~ 4 
1-09 x HD 4 
Emission 
divided by 
(0 4 -0o 4 ). 
9 • 373 x 10 -13 
9-94 x 10~ 13 
9-64 x 1CT 13 
October 29, 1889 . 
0-45 
99-0 
72-0 
56-0 
15-3 
1-25 x HT 4 
1■14 x10~ 4 
1•03 x1CT 4 
8-55 xlO" 13 
8-89 x 10 -13 
8-73 x 10 -13 
April 2, 1890 
April 8, 1890 
0-8 
116-0 
101-5 
85-0 
16-0 
1-57 x10“ 4 
1-43 x10“ 4 
l-24x 10“ 4 
9-82 x 10~ 13 
9-64 x 10 -13 
9-03 x 10~ 13 
0-2 
96-4 
86-6 
78-2 
r 1-22X10- 4 
15-0 1 • 26 x 10~ 4 
L 1 -07 x10 -4 
8- 58 x 1CT 13 
9- 17 xHT 13 
8-12 x 1CT 13 
From these tables, given complete on p. 371, I have extracted numbers corresponding 
’ to temperatures between the limits 0° C. and 100° C. It will be seen that the values 
I have obtained for Stefan’s coefficient are also lower than those which they have 
obtained at similar temperatures ; but my numbers do not differ so much from the 
results of Graetz and Kundt and Warburg as do those of Christiansen and 
Kurlbaum from the results of the last-named observers. 
The accompanying sheet of curves brings out some of the relations of the numbers 
under consideration in a somewhat interesting way. Taking the Stefan coefficient to 
be 9 x 1 0 -13 , and taking the temperature of a sooted enclosure such as I used in my 
experiments to be 80° absolute, I have calculated corresponding emissivities; 
and on plotting these they form curve I. on the sheet. To compare these with 
emissivities obtained by experiment, I have laid down the results of the experiments 
of Mr. King and myself of dates July 5, 1904, and June 28, September 18, 1906. In 
each case the surrounding envelope was at the temperature of liquid air. In one case 
the vacuum was 0T8 M., and in the other it was absolutely unmeasurable, and as 
nearly perfect as can be obtained by the use of charcoal and liquid air. I have also 
traced the curve for my old results of April 8, 1890, where the temperature of the 
enclosure was 15° C., or 288° absolute, and the vacuum was 0 2 M. N ow com¬ 
paring the curves for July 5 and September 18, it will be seen that the emissivity in 
the case of the former at 0'18 M. is rather more than double that at the nearly 
perfect vacuum ; and it seems not unnatural to suppose that, if I had been able to 
improve correspondingly the vacuum of April 8, the emissivity would have been 
reduced to less than half of that which I found. I have other evidence that this 
supposition is very close to the truth. If the circumstances under which this 1890 
experiment was carried out had been precisely comparable with those represented by 
